Generally, marine running lights on larger vessels and workboats such as Tug boats mostly operate off 120 VAC. Many of these boats have alarm panels that sound an alarm if one of the running lights burns out. As long as the current drain appreciably drops close to zero, then the alarm panel can detect that a light is burned out. In these systems, each light is connected to its own circuit so if current drain drops appreciably almost to zero an alarm indication is displayed. Also, a break in the wiring can drop the current to zero and cause the panel to sound the alarm.
Typically, most of the lights on workboats are operated off 120 VAC, therefore a single lamp runs on one circuit. When a filament of a light burns out, the current immediately drops to zero and an alarm panel can detect the drop in current and sound an alarm for the burned out lamp. An alarm panel may, for example, detect a drop in current directly. Alternatively, an alarm panel may detect a loss of a voltage drop across a resistor, such loss corresponding to a drop in current.
With the implementation of LEDs into these types of circuits, a low voltage supply is required. Also, the LEDs drain much less than incandescent lamps so the alarm panels would indicate lamp failure even though the LEDs were still giving off light. One way of obtaining low voltage is by use of a step down transformer. However, transformers have idle currents, or eddy currents, and therefore there would be a current in the primary winding when no load is connected to the secondary winding of the transformer. Under these conditions, alarm panels will not detect a burned out LED or low voltage incandescent bulb because there is always some primary current. Unfortunately, this primary current is considerable and unless the alarm panels are adjusted precisely, an alarm will not sound. This makes operation of the alarm panels presently in use virtually impossible or impractical with these new types of LEDs or low power incandescent lights.
With reference to FIG. 1, a typical alarm panel circuit 100 with a current sensing relay is illustrated. In FIG. 1, when current I passes through relay coil 110, contacts 120 will remain open. Incandescent lamp 130 is connected to relay coil 110 and contacts 120 through equipotential points 150 and 160. If there is a break in the wiring or incandescent lamp 130 fails, the current drops, which causes contacts 120 to close and alarm 140 to sound. Incandescent lamp 130 may operate on either 120 VAC or 12 VDC. With reference to FIG. 2, a typical alarm panel circuit 200 with a voltage sensing device, such as a comparator, rather than a current sensing device, is illustrated. In FIG. 2, when current flows through electrical circuit 200, incandescent lamp 210 is lit and there is a voltage drop across resistors 220 and 222. Incandescent lamp 210 is connected to the other portions of electrical circuit 200 through equipotential points 260 and 270. Incandescent lamp 210 may operate on 120 VAC or 12 VDC. As long as this voltage appears across resistor 220, comparator 230, which compares the voltage between + and −, keeps transistor 240 on and the circuit to alarm 250 open. If, however, the voltage drop across resistor 220 falls below a predetermined threshold value due to a failure of incandescent lamp 210 or wiring problems, comparator 230 turns transistor 240 off, which closes the circuit causing alarm 250 to sound thereby indicating that incandescent lamp 210 is out.
These and other panel designs do not function properly when attached to LEDs, or low voltage incandescent lamp circuits. Similarly, LEDs and low voltage incandescent lamps cannot be installed in conjunction with presently available alarm panels.
LED lamps generally have the following characteristics: LEDs that are not emitting light can nevertheless drain the same amount of, or more, current than LEDs that are emitting light. Because of this, alarm panels will not sound an alarm even though the LEDs are not emitting any light. Also, LEDs require low voltage to operate and a common way of producing low voltage is a step down transformer. However, transformers have current through their primary winding, which indicates no light failure to the alarm panels even though there may be no load on the secondary winding and the LEDs may not be emitting any light. Under these circumstances, a boat would have no navigation light but the alarm panel would not indicate that a problem exists.
Therefore, it would be desirable if boats equipped with alarm panels could accommodate LEDs such that the LEDs would work on the panels without any modification. It would also be desirable if this system could work on low voltage incandescent types of fixtures.